The present invention relates to a stabilizer bar. The stabilizer bar is intended for use in vehicles, particularly in heavy vehicles. A stabilizer bar of the indicated kind comprises a metallic tube having a central portion and at least two bent portions forming legs, each leg of the tube forming and an angle with the central portion of the tube.
The invention further relates to a method, for manufacturing stabilizer bars or similar tubular metallic products. According to such a method, the ends of a metallic tube are bent at a suitable angle in relation to the central portion of the tube, the ends of both the legs formed being subsequently provided with suitable means for fastening of the stabilizer bar to the chassis (frame) of the vehicle.
Finally, the invention also relates to an apparatus, for manufacturing stabilizer bars.
Stability improving stabilizer bars are commonly used in trucks, especially in heavy trucks having a total weight of up to 58 tons. In order to increase the payload of the trucks, the maximum gross vehicle weights permitted for trucks have been raised at the same time as the vehicle weights have decreased. In order to maintain the suspension comfort, air suspension or, alternatively, parabolic springs with few leaves have been introduced in trucks. This development has resulted in the center of gravity of the vehicles being shifted upwards, which already by itself increases the instability of the vehicles, in particular since the springs have been dimensioned more and more only for the purpose of suspension. The requirement for good stability, that is anti-roll stiffness, has remained and PG,3 even been increased due to increasing speeds. This is the reason for wanting to eliminate the instabilizing effects caused by the above-mentioned reasons by increasing the stiffness of the stabilizer bars.
Stabilizer bars for heavy trucks have mostly been manufactured from solid round steel bars. So far the diameters of the bars have been about 50 mm. The requirement for increased stiffness is leading to a need for diameters up to 70 mm. This 40% increase of the diameter is leading to a 100% increase of the weight of stabilizers bar made from steel bars. Because more and more axles of the vehicles are nowadays provided with stabilizer bars, the requirement for increasing roll stiffness is leading to an unaccepted growth of the vehicle weight.
One possible solution to this problem is the use of tubes instead of solid bars as raw materials for the stabilizer bars. Tubular products have so far been produced on a smaller scale for the indicated purpose. Although it is possible, in theory, to attain a weight reduction of up to 50%, there are several reasons why the tubular stabilizer bars have not been a success on the market.
The stress on a stabilizer bar is highest in the bends, which means that the shape of the bends is crucial. The utilized tube bending methods, primarily different forging methods, have given rise to weak bends due to unfavourable distribution of the material in the bends. It has also been difficult to achieve bends with sufficient short radii (narrow bends) while maintaining the circular cross sections of the bends.
Thus, by using conventional forging methods, it is not possible to obtain bends which simultaneously fulfil the requirements for the desired bending radii, the circular shape of the cross section and the distribution of the material in the bends. This is why the technical-economic competitiveness of the tubular stabilizer bars has not been strong enough for the tubular stabilizer bars to gain on the solid ones on the market.
The present invention aims at eliminating the drawbacks of the previous methods and at providing an entirely novel tubular stabilizer bar. The invention also aims at providing a novel method and a novel apparatus for manufacturing these kinds of stabilizer bars.
By means of experiments, we have been able to ascertain that satisfactory results can be achieved by using a bending method known as induction bending, provided that the bending process is operated so that a combination of bending and controlled upsetting of the inside of the bends takes place at the same time. This way a cross section with a very little deviation from the circular shape can be obtained at the same time as the stretching of the outer wall of the bend can be reduced.
For the purpose of this invention, thick-walled tubes are utilized, the tubes being shaped by the induction bending technique to stabilizer bars.